Compositions of epoxy resins with 2,6-diketo-n-carboxymethylmorpholine

ABSTRACT

EPOXY RESINS CAN BE CURED WITH 2,6-DIKETO-N-CARBOXYMETHYLMORPHOLINE AS THE SOLE CURING AGENT TO PRODUCE FULLY CURED, STRONG AND HARD COMPOSITIONS.

United States Patent Office 3,689,456 Patented Sept. 5, 1972 US. Cl.260-47 EN 2 Claims ABSTRACT OF THE DISCLOSURE Epoxy resins can be curedwith 2,6-diketo-N-carboxymethylmorpholine as the sole curing agent toproduce fully cured, strong and hard compositions.

REFERENCE TO PRIOR APPLICATION This is a division of copendingapplication Ser. No. 740,853, filed June 28, 1968, now US. Pat.3,621,018.

BACKGROUND OF THE INVENTION It has not previously been possible toprepare 2,6- diketo-N-carboxymethylmorpholine, hereinafter referred toas NTA anhydride, because conventional dehydrating techniques result ina variety of side reactions. A new process has been found by which NTAanhydride can be produced. The anhydride is useful as an epoxy curingagent.

It is the object of this invention to provide a new composition ofmatter, namely 2,6-diketo-N-carboxymethylmorpholine. It is also theobject of this invention to provide a process for producing the NTAanhydride. It is a further object of this invention to provide a newcuring agent for epoxy resins. Other objects will become apparent tothose skilled in the art from the following detailed description.

SUMMARY OF THE INVENTION This invention relates to NTA anhydride, theprocess for producing NTA anhydride and to uses of the anhydride. Moreparticularly, this invention relates to a new composition of matter, NTAanhydride, which is produced by a process which comprises contactingnitrilotriacetic acid in a suitable reaction media, preferably anN,N-dialkylacetamide, with a dehydrating agent, and to the uses of theNTA anhydride so produced.

DESCRIPTION OF THE PREFERRED EMBODIMENT A new composition of matter, NTAanhydride, is produced by a process which comprises contactingnitrilotriacetic acid in an N, N-dialkyl acetamide with a dehydratingagent. The alkyl substituents can contain 1 to 6 carbon atoms such asmethyl, ethyl, amyl, hexyl, and the like, and the preferred acetamide isN,N-dimethyl acetamide. The nitrilotriacetic acid can be dissolved inthe acetamide or in a mixture of the acetamide and the dehydratingagent. The nitrilotriacetic acid generally comprises about 1 to about 80weight percent of the nitrilotriacetic ac'id-N,N-dialkyl acetamidesolution, and is preferably from about 10 to about 50 weight percent.

Conventional dehydrating agents can be employed to convert thenitrilotriacetic acid to its anhydride. Typical dehydrating agentsinclude organic anhydrides such as acetic anhydride, propionicanhydride, maleic anhydride, succinic anhydride, and the like; enolesters such as isopropenyl acetate and the like; organic acid chloridessuch as acetyl chloride and the like; P 0 and the like dehydratingagents. The preferred dehydrating agent is acetic anhydride. The ratioof moles dehydrating agent to moles nitrilotriacetic acid can vary from1:20 to 20:1. It is preferred to use near the stoichiometric quantity ofdehydrating agent, i.e., a ratio of about 0.75 to about 1.25 molesdehydrating agent to one mole of nitrilotriacetic acid.

A typical synthesis procedure can comprise fitting a reaction vesselwith a stirrer, nitrogen inlet tube, thermometer, and a steam jacketedpartial condenser fitted to a water condenser and water trap. Thenitrilotriacetic acid, N,N-dialkyl acetamide and dehydrating agent arecharged into the vessel and heated under agitation and inert nitrogensparge until the reaction reaches the desired level of completion, asconveniently measured by the acid number technique. The excess reagentscan be removed by conventional techniques, such as steam distillation,and the NTA anhydride recovered by conventional techniques, such asprecipitation. The reaction mixture can be heated from about 50 to aboutdegrees centigrade, preferably about 70 to about 100 degrees centigrade.The time necessary to complete the above-described reaction can varyfrom 0.5 to 24 hours, although times of 2 to 10 hours are preferred.

The NTA anhydride can be employed as a curing agent for any of thosematerials known in the art as epoxy resins. Included in thisclassification are resins such as the well-known reaction products of adihydric phenol and a halohydrin, epoxidized hydrocarbons, epoxidizedvegetable oils, as well as naturally occurring materials of the sametype containing the oxirane ring structure. By the terms epoxy resin orpolyepoxide as used herein, is meant the compounds which containadjacent carbon atoms to which oxirane oxygen is attached. The epoxyresins that are the reaction products of a dihydric phenol andhalohydrin are generally obtained by reacting at a temperature of about50 to degrees centigrade at least one mole of the halohydrin, such asepichlorohydrin, glycerol dichlorohydrin, 3-chloro-1,2-pr0panediol, andthe like, with one mole of the dihydric phenol, such as resorcinol,dihydroxy diphenyl propane, polyhydric phenol formaldehyde condensationproducts, and the like, in the presence of an alkali metal hydroxidesuch as sodium and potassium hydroxide or an alkaline earth hydroxidesuch as calcium and barium hydroxide. The epoxy resins which are formedby epoxidizing unsaturated hydrocarbons can be prepared, for example, byreacting the unsaturated polyolefin, such as polyvinylcyclohexene,polychloroprene, polyisoprene, polybutadiene, and the like, with asuitable reactant such as acetyl peroxide for several hours at anelevated temperature. Another type of epoxy resin useful in thisinvention are the polyepoxides derived from naturally occurringvegetable oils, or their derivatives, such as epoxidized soy bean oil,epoxidized linseed oil, epoxidized glycerol dilinoleate, and the like.Such materials are prepared, for example, by agitating the compound tobe epoxidized with a peracetic acid solution, prepared from glacialacetic acid, 30 percent hydrogen peroxide and 1 percent sulfuric acidcatalyst.

In the practice of the invention, the NTA anhydride curing agent ismixed with the desired uncured epoxy resin at room temperature or at anelevated temperature. The curing agent is preferably incorporated in anamount from about 2 to about 40 parts by weight per 100 parts of uncuredepoxy resin, and preferably from about 5 to about 15 parts by weight.The curing temperatures vary over a wide range from 50 to about 250degrees centigrade, but are preferably in the range of about 100 toabout 200 degrees centigrade. The time necessary to effect curing varieswith the particular ingredients of the curing system, from severalminutes to several days, however, it is preferably from about 0.5 toabout 48 hours.

The NTA anhydride can also be used as a chemical intermediate inpreparing useful chemical derivatives not easily prepared by othermethods. The following reactions are typical:

PREPARATION OF NTA ANHYDRIDE Example 1 A charge of 191 partsnitrilotriacetic acid, 348 parts N,N-dimethyl acetamide and 306 partsacetic anhydride were placed in a vessel equipped with a thermometer,nitrogen inlet tube, stirrer, reflux condenser, and heating means. Anitrogen sparge was employed and the vessel heated to about 90 degreescentigrade for about 4 hours. Thereafter, the acetic acid, unreactedacetic anhydride and N,N-dimethyl acetamide were removed at 75-84degrees centigrade under reduced pressure. The residue in the vessel wasfound to contain about 75 percent NTA anhydride.

Example 2 A slurry of 191 parts nitrilotriacetic acid, 110 parts aceticanhydride and 355 parts N,N-dimethyl acetamide was stirred for about 7hours at 80 degrees centigrade. A small amount of the unreactednitrilotriacetic acid was filtered from the resultant reaction mixtureand most of the volatiles removed at 70-80 degrees centigrade underreduced pressure. The residue was stirred with 300 parts of chloroform,filtered, and the resulting solid was thoroughly washed with 300 partsof chloroform. The resulting product was dried in vacuum at ambienttemperatures to produce an off-white solid having a decomposition pointof 121-124 degrees centigrade. The product was further purified bysolution in acetone, in which the nitrilotriacetic acid is insoluble andthe anhydride is soluble. The product, NTA anhydride(2,6-diketo-N-carboxymethylmorpholine), was obtained in about 70 percentyield and 96-97 percent purity. The NTA anhydride was furthercharacterized by the following analysis:

Elemental analysis-Calculated (percent): C, 41.7; H, 4.1; N, 8.1. Found(percent): C, 41.7; H, 4.2; N, 8.1.

Nuclear magnetic resonance: two singlet peaks in an area ratio of 2:1are found at 3.90 and 3.60 ppm. relative to tetramethylsilane.

Titration: base titrations, aqueous and nonaqueou showed the presence ofone anhydride group and one carboxyl group, and were consistent with theassigned structure, viz

Infrared: strong absorption bands at 1710, 1770 and 1805 cm. (nujolmull), showing the presence of anhydride and carboxyl groups.

Example 3 The process of Example 2 can be repeated using anitrilotriacetic acid which has been prepared externally or in situ fromthe corresponding nitrilotriacetic acid alkali metal salt, to obtain thecorresponding nitrilotriacetic acid anhydride.

NTA ANHYDRIDE AS AN EPOXY CURING AGENT Example 4 Ten parts of the NTAanhydride of Example 2 was mixed with 10 parts of the diglycidyl etherof Bisphenol A at ambient temperatures. The mixture was subjected to atwo-stage cure of 24 hours at degrees centigrade followed by 24 hours at120 degrees centigrade. A strong, hard, fully cured epoxy resin wasobtained.

NTA ANHYDRIDE AS AN INTERMEDIATE Example 5 A mixture of 8.7 grams NTAanhydride and 50 ml. methanol was stirred for 4 hours at roomtemperature. Thereafter, 6.9 grams (68 percent yield) of melting at110-120 degrees centigrade was recovered.

Various modifications can be made in the invention, without departingfrom the spirit and the scope thereof. Various embodiments of theinvention disclosed herein serve to further illustrate the invention butare not intended to limit it.

We claim:

1. A composition comprising an epoxy resin which contains adjacentcarbon atoms to which oxirane oxygen is attached and a curing amount of2,6-diketo-N-carboxymethylmorpholine.

2. The composition of claim 1 wherein the 2,6-diketoN-carboxymethylmorpholine is present in an amount from about 2 to about40 parts by weight per parts of uncured epoxy resin.

References Cited UNITED STATES PATENTS 3,419,525 12/1968 Aelony 260-47WILLIAM H. SHORT, Primary Examiner T. E. PERTILLA, Assistant ExaminerUS. Cl. X.R.

1l7--l61 EZ; 260-2 EA, 2 N, 18 Ep, 47 EA, 92.3, 93.1, 94.7 N

